More on anti-histamines in Autism and introducing H4

In my previous posts on histamine, you would have read that I found that Claritin appeared to reduce autistic behaviours.  Once I had got to the bottom of what was going on, I found out that histamine has a long record of stimulating challenging behaviour in all children.  It also became clear that typical anti-histamines (H1 antagonists) are all slightly different and one may be effective in one person and ineffective in another.  Each one tends to have additional secondary effects.

It now appears that the secondary effect of certain H1 antagonists may actually be more important than the primary intended effect of reducing itchy eyes and runny noses.

There are three generations of H1 drugs.  The fastest working and most potent is still the first generation, the second generation are non-drowsy derivatives of the first generation.  The third generation are the active metabolite of the second generation.  As you will see in today’s central paper, the third generation probably does not warrant the tittle.  For many users they may be just expensive versions of the second generation drug.

The excellent paper  New anti histamines: a critical view is from Brazil, but it has an English version.  It is highly readable.  It tells of the specific secondary effects of certain second generation  H1 antagonists.   (She omits to mention the secondary effects of the first generation. Some people say Ketotifen is 1^st generation and other people say 2^nd generation, anyway it appears not to be sold in Brazil).  I suggest you read the paper, if you have a child with an ASD. The key section is this:

Antiallergic/anti-inflammatory effects

Originally, studies of the relative potencies of H1 antihistamines were based on the capacity of different compounds to competitively inhibit the H1 receptor binding of histamine, i.e. on their blocking effect on the receptor.⁸ Nevertheless, it has already been known for some time that, in addition to acting on H1 receptors, many H1 antihistamines, at appropriate doses, are capable of inhibiting not only the release of histamine by mast cells,^9,10 but also mast cell activation itself.¹¹ Some of them can even regulate the expression and/or release of cytokines, chemokines, adhesion molecules and inflammatory mediators.^5,8

Therefore, the antiallergic properties of H1 antihistamines are generally a reflection of their capacity to affect mast cell and basophil activity, inhibiting the release of preformed mediators such as histamine, tryptase, leukotrienes and others.⁸ Several second-generation H1 antihistamines have demonstrated antiallergic properties, irrespective of their interaction with the H1 receptor.^5,8

Chronic allergic inflammation resulting from the late-phase reaction, exhibits components that are similar to other forms of inflammation, including chemotaxis of inflammatory cells followed by activation and proliferation, with subsequent production and release of many chemical mediators. Among cells involved in allergic inflammation are: antigen-presenting cells (for example, macrophages), mast cells, basophils, T lymphocytes, epithelial/endothelial cells and eosinophils - major effectors of chronic inflammation. Cytokines, chemokines, inflammatory mediators and adhesion molecules also contribute to this process which ultimately leads to dysfunction of the affected organ.⁸

Many second-generation H1 antihistamines (particularly cetirizine) are capable of inhibiting the influx of eosinophils to the site of allergen challenge in sensitized individuals.^5,8 Studies have demonstrated that some of them can also alter adhesion molecules expression on epithelium and eosinophils, and reduce in vitro survival of eosinophils. Finally, some second-generation H1 antihistamines are capable, in vitro and in vivo, of altering the production of inflammatory cytokines (for example, TNF-a, IL-1b and IL-6) and the Th1/Th2 balance regulation cytokines (for example, IL-4 and IL-13).^5,8

Therefore, it is well established that, in addition to their effects on H1 receptors, many second-generation H1 antihistamines also manifest antiallergic and anti-inflammatory properties which differ depending upon their molecules and the experiments used for their evaluation.⁵

 

From my own experience, I have already replaced Claritine (Loratadine) with Cetirizine to see if it will remain active for longer.  Rather than working for 24 hours, Claritine is working for about 5 hours.

I thought Cetirizine might remain active for longer, but the main difference seems to be in how it works, rather than for how long it works.  With Cetirizine autistic behaviour has pretty much returned to where it was at the start of summer, before the allergy season.  With Claritine things improved greatly, but not all the way back to "normal".

Reading the paper and one of its references -

Compared pharmacological characteristics in humans of racemic cetirizine and levocetirizine, two histamine H1-receptorantagonists

makes me think that the expensive new  version of Cetirizine, called Levocetirizine, might be even better.  It happens to be available locally, but it is seven times as expensive.

The Brazilian paper does rather contradict some of what Dr Theoharides says about stabilizing mast cells.  You can choose who you think has got it right.  The good thing is that both Dr Inês Cristina Camelo-Nunes and Dr Theoharides seem very serious, objective people, which cannot be said about all the people offering their advice on the internet.

In fact, I found an interesting paper on the anti-inflammatory effects of the new version of Claritin, called Aerius/Clarinex (Desloratadine).

Antihistaminic, Anti-Inflammatory, and Antiallergic  Properties of the Nonsedating Second-Generation Antihistamine Desloratadine: A Review ofthe Evidence

It really seems to be the case of trying several antihistamines and selecting the one that works best for you.

 

The H4 Histamine Receptor and Inflammation

You may recall that there is a fourth histamine receptor, naturally called H4.

It was only recently discovered, as you might guess from the short entry in Wikipedia.  It seems that the H4 receptor plays a substantial role in the inflammatory response.  It is seen as playing a key role in conditions ranging from arthritis to asthma.

Here is a full text paper for those interested in the science:-

The role of histamine H4 receptor in immune and inflammatory disorders

 Here is a graphic from that paper:-

I wonder if that H4 is a ticking bomb in autism as well ?

Those more peaceful people among you will be less aware of what C4 is, and hence the sticks of H4 dynamite.