senior cat care, The Feline Purrspective

If you search for “monoclonal antibodies”, most of the search results are about COVID-19 and its variants. But did you know that monoclonal antibodies form the basis of the newest treatment for arthritis in cats? This new treatment is called Solensia. Solensia is a monthly injection for arthritic cats that won FDA approval this month. It should be available through your veterinarian later this year.

arthritis in cats: a tale of biotech and a chinese hamster

what are monoclonal antibodies?

Monoclonal: refers to a cell or organism that comes from a single individual or cell.
Antibodies are proteins in the blood that our immune system produces to counteract a foreign substance such as a bacteria or virus (think COVID-19).

antibodies and the immune system

Immune cells in our bodies called B-lymphocytes mount a response to a foreign substance or antigen (e.g. a virus), binding to it and deactivating it. The presence of the antigen and immune cells called T cells activate the B-cells. The B cells then propagate and release antibodies that are able to bind to and deactivate the specific antigen that stimulated their formation!

Monoclonal antibodies are derived from clones or copies of activated B cells. They can be harvested and grown in the laboratory and used to fight infections caused by the antigen they were developed to target.

Where do monoclonal antibodies come from?

Blood cells from convalescing patients: Due to the large numbers of convalescing COVID patients, there was a ready source of blood cells containing B-cells with antibodies to COVD 19 that could be used to make monoclonal antibodies to treat newly infected patients.
Transgenic mice: Mice that have been genetically altered to carry human antibody genes instead of mouse antibody genes are the usual source for monoclonal antibodies. These mice can be injected with a specific antigen and produce fully human antibodies that can be used by human patients to combat that antigen. Being human antibodies, they are less likely to be rejected by the human immune system.

Arthritis in cats: using monoclonal antibodies

Nerve growth factor (NGF) is a protein that is key to the development and survival of nerve cells or neurons, particularly sensory neurons that transmit pain, temperature, and touch sensations.

When NGF binds to pain receptors inside the sensory neuron, a series of events is triggered that ultimately sends a “pain” signal to the brain.

Instead of binding to a structure on a virus, monoclonal antibodies can be developed to recognize and attach to NGF, preventing NGF from binding to the pain receptors on the sensory neruron, blocking the pain signal.

Motion is Medicine

A reduction in pain means our arthritic cats will be more likely to move around more. Increased mobility will strengthen the cat’s muscles, so they can better support and assist the deteriorating joints. Increased activity and reduced pain result in a better quality of life.

Biotech Magic

The active ingredient in Solensia is frunevetmab, a monoclonal antibody that targets NGF. The antibodies are sourced from Chinese hamster ovary cells. Like the mice that have human antibodies instead of mouse antibodies, the hamster cells are “felinised”using recombinant biotechnology. Sections of the hamster antibodies are replaced with their feline counterparts. “Felinization” ensures that the cat’s immune system will not reject the monoclonal antibodies but allow them to function as part of the cat’s immune system.

Of cats and hamsters: no hamsters harmed

Frunevetmab is sourced from the cells of Chinese hamster ovaries. In fact, cells from an individual Chinese hamster, harvested back in the 1950s, produced the cell line which dominates biotechnology today. These cells are easy to propagate and maintain in the lab, providing a ready source of monoclonal antibodies.

multimodal therapy for arthritis in cats

Solensia is a pain medication and does not directly aid in preserving the synovial tissues. Most likely, Solensia will be part of a multimodal treatment that will include drugs and supplements like Adequan or glucosamine that are thought to help maintain synovial tissues in addition to weight loss and exercise.

Unlike other arthritis pain treatments such as NSAID’s, monoclonal antibodies are eliminated in the same way other proteins are, with minimal effect on the kidneys and liver, a concern for our cats with Chronic Kidney Disease.

Treatment using Solensia will consist of monthly injections under the skin. Most cat owners can become proficient in giving subcutaneous injections and treatment can be done in the safety and comfort of the cat’s home.

Thanks to a Chinese hamster years ago and advances in biotechnology, our cats may be able to spend their “ golden years” without pain from osteoarthritis!

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HDO BP cat — A cat relaxes in his basket during a blood pressure reading at home using an HDO unit. The cuff is on his tail. The blood pressure wave is on the computer screen.

You’ve brought your senior cat in for her regular checkup and the technician asks you if you would like to have her blood pressure checked. Although your blood pressure is routinely checked when you go to the doctor, it has not occurred to you to ask to have your cat’s blood pressure checked. Should you have your cat’s blood pressure measured? How is it done – will it be uncomfortable? Frightening?

Why measure your cat’s blood pressure

As cats age, many develop hyperthyroidism and kidney disease. Other cats may develop diabetes. All of these conditions can result in the heart pumping harder to compensate for the changes. As the heart pumps harder, blood pressure increases and arteries, the eyes, the kidneys, the brain and heart can be damaged.

Left untreated, high blood pressure can result in:

blindness
increasing loss of protein through the kidneys >> shortened life span
disorientation, lack of balance, seizures, altered mentation or behavior, or weakness in the limbs

The best way to avoid these consequences is to monitor your cat’s blood pressure and start treatment if his blood pressure is high.

So how do we measure your cat’s blood pressure?

When measuring blood pressure in humans, we typically place a pressure cuff on the upper arm, inflate the cuff until the flow of blood to the artery is shut off . The cuff is then released, and a wave of blood fills the artery, turbulent at first, then subsiding to a smooth flow.

The human practitioner can use a stethoscope to listen to the sounds made as the blood rushes back into the artery.

The first sound is heard at the systolic blood pressure (the higher number in 120/80)
The final sound is heard at the diastolic pressure (the lower number in 120/80).

We will also use a blood pressure cuff to measure your cat’s blood pressure. This cuff can be put:

on the front leg
on the hind limb, above or below the hock (ankle)
on the tail

Cats’ arteries are much smaller than humans’ and it is difficult to hear the sounds of the blood flow using a stethoscope, so we turn to other methods: Doppler and oscillometric.

Doppler

A Doppler unit measures blood flow.

After placing the cuff on your cat, the Doppler sensor is placed over the target artery.
Piezoelectric crystals in the sensor detect changes in the flow of blood in the arteries and convert these to sound.
Acoustic gel on the sensor ensures good contact so that the practitioner can hear the heartbeat.
The cuff is inflated until the heartbeat is no longer heard.
The cuff is then released and the pressure at which the heartbeat can be heard again is the systolic blood pressure.
Headphones are usually used when measuring blood pressure with a Doppler.

Doppler units give us a measurement of the systolic blood pressure, the larger number in the 120/80.

Oscillometric

Only a cuff needs to be placed to measure your cat’s blood pressure with an oscillometric unit.

A sensor in the cuff detects the pressure pulses in the artery.
As the cuff is inflated, the pulses decrease as flow to the artery is cut off.
The cuff is then deflated and the pressure wave that results as the blood rushes back into the artery is analyzed.

Oscillometric units typically only measure the peak of this wave, the average blood pressure, and calculate the systolic and diastolic pressures.

A High Definition Oscillometric unit records the entire pressure wave, directly measuring the systolic and diastolic pressures. An HDO unit is usually connected to a computer to view the pressure wave and determine if the measurement was accurate.

How accurate is a blood pressure if my cat is nervous at the vet clinic?

Just like people, cats get anxious and nervous when visiting the vet clinic. Blood pressure is sensitive to this and it can be a challenge to measure your cat’s blood pressure.

Putting the odds in our favor:

Most of the time, you should be with your cat during a blood pressure measurement. Your cat knows you and trusts you. Your presence is reassuring and calming.
Allow your cat to settle in for 5-10 minutes – the measurement should be done in a quiet room.
If your cat likes to snuggle in your lap, see if the measurement can be done there. If your cat prefers to sit on his stomach, perhaps a tail measurement is best. If he is comfortable laying on his side, a hind leg may be better.
Using the front leg to measure blood pressure puts the practitioner in front of the cat; curious cats may want to take a nibble at the blood pressure cuff. I prefer that your cat be facing you, her person, who can reassure her. I feel the tail and hind leg work better.
The artery being measured, tail or hind leg, should be at the same level as the heart – so kitty should not be sitting up, but laying comfortably on his stomach or side.

What do the numbers mean?

Again, like people, the systolic pressure is ideally around 120.
Pressures 150 and over can indicate the need for medication.
Your vet may also do an eye exam, looking at the eye with an ophthalmoscope or lens. In some instances of high blood pressure, the vessels in the eye dilate and become twisted; sometimes the retina may be detached, resulting in blindness. If high blood pressure is caught early enough, blindness may resolve with treatment.

My cat’s blood pressure is high but her eyes looked OK. What next?

High blood pressure can be treated with drugs – the most common drug used is oral amlodipine. Amlodipine takes effect fairly quickly and a blood pressure can be repeated in about 10 days and the dose adjusted if needed.
Other medications such as benazepril or telmisartan may be used alongside or in place of amlodipine.

I don’t think the reading was accurate – my cat was too nervous

It is worth investing in a home blood pressure visit. A practitioner can come to your home and get a measurement where your cat feels safe and secure.

Measuring your cat’s blood pressure especially as she gets older will help keep her healthy and comfortable. Without treatment, high blood pressure can have serious side effects, including blindness, seizures, and cardiac damage.

Have your cat examined regularly by your veterinarian, as changes to the eyes or a heart murmur might warrant a blood pressure check.